Ultrasound systems have a wide range of applications including, for example, medical procedures for imaging, diagnosis, or treatment of a human body. Using an ultrasonic transducer, energy can be transmitted to adjacent tissue so that the energy can be absorbed by parts of the body.
The concept of using ultrasound radiation to remove unwanted hair appeared in the literature as early as 1998. (Iger et al., WO 00/21612 “A Method and Device for Hair Removal,” “Iger” hereinafter.) The underlying principal is to use ultrasound radiation to selectively induce damage to the hair structure and thereby retard its ability to regenerate. Typically, the bulb or bulge of the hair follicle is targeted since these features are thought to be involved in the regenerative process of hair growth. These features are commonly located several millimeters below the skin surface.
To date, two main techniques have been proposed for delivering the radiation to the hair follicle. In one, the hair shaft is gripped above the skin by some mechanical means and radiation is then coupled directly into either the side or end of the hair shaft. (See, e.g., Barzilay et al., U.S. Patent Application 2007/0173746 “Method and Device for Removing Hair,” “Barzilay” hereinafter.) An ultrasonic transducer then focuses the radiation into the shaft, which transmits the energy to the hair follicle below. Alternatively, the radiation may be focused through the skin to a point of high intensity on a hair follicle. (See, e.g., Masotti., WO 02/09813 “Method and Device for Epilation by Ultrasound,” “Masotti” hereinafter.) Since the targeted location is typically several millimeters below the skin surface, the practical limits of beam focusing requires that the beam radius on the skin surface to be less than several millimeters wide.
These beam delivery methods are similar in that they both use a form of spatial selectivity to concentrate the radiation within the hair structure, and thereby damage it, without affecting the surrounding tissues. In addition, both techniques focus the beam onto the hair to generate the intensity required to create damage. Two advantages of this approach are: 1) the target is located in the far-field of the transducer (close to the focal plane) where the beam's intensity profile has a smooth shape; 2) a low-power transducer is required since the output intensity at the transducer is significantly lower before it is focused. However, the inherent spatial selectivity prevents the application of these techniques to treating many hairs simultaneously. In particular, the wide variability in the spacing, angle, and length of hair shafts makes it impractical to grab, position, and efficiently irradiate a large number of hairs at one time. Because the spacing of the hairs may vary slightly, it is also impractical to design a device with multiple focal points aligned to individual follicles.
This lack of scalability makes these techniques unsuitable alternatives to existing light-based technologies that are capable of treating large areas in a short period of time. For example, common areas for light-based hair removal treatments include the axilla (armpit), arms, legs, back, chin, and pubic areas where the hair density ranges from 50 to 500 follicles/cm2. (Helen R. Bickmore, Milady's Hair Removal Techniques: A Comprehensive Manual, Thompson Learning Inc. (2004).) Using light-based technologies, the typical treatment area may range from 1 to more than 100 cm2, and the treatments can be performed at speeds up to 3 cm2/sec. As a result, using light-based technologies, 50 to 50,000 hairs may be treated in a period between 1 and 33 sec.
What's needed is an ultrasonic device that can deliver performance comparable to existing light-based techniques. Specifically, there is a need for an ultrasonic device that can treat multiple hairs using a wide-area exposure. Preferably, a device should have an effective treatment area of about 1 mm2 or greater since this would allow treatment of at least 5 hairs at one time.